In many types of electronic circuit applications, it is necessary to provide at least two power supplies: a positive voltage power supply and a negative voltage power supply. In BiCMOS circuits, for example, it is typically necessary to provide both positive and negative bias voltages for providing power to the various circuit elements.
The use of two power supplies is expensive both in terms of the power supplies themselves, and the layout and formation of the voltage distribution lines necessary to distribute the two voltages. This layout and distribution requires not only substantial planning and design, but a significant percentage of available wiring.